Intended Flap Decentration in Hyperopic Laser in Situ Keratomileusis ( Lasik ) In Eyes with off-Centered Corneal Apex

Purpose: To evaluate the efficacy of flap decentration during Lasik hyperopic correction in eyes with off-centered corneal apex. Patients and methods: In a prospective study, two groups of patients with hyperopia randomly allocated to undergo Lasik hyperopic correction. In group A (22 eyes); the flap was intentionally decentred during flap creation. In group B (22 eyes) were done without flap decentration. Complete preoperative and postoperative ophthalmic examination was done for all patients with determination of spherical equivalents by cycloplegic refraction, Uncorrected Visual Acuity (UCVA), Best Corrected Visual Acuity (BCVA) were also detected. Corneal topography was performed to all patients before and after the operation. Results: The mean UCVA improved from 0.4 ± 0.23 to 0.90 ± 0.21 in Group (A) and from 0.5 ± 0.3 to 0.8 ± 0.2 in Group (B) (P value = 0.023), and the mean BCVA, from 0.8 ± 0.2 to 0.97 ± 0.1 and from 0.8 ± 0.2 to 0.8 ± 0.2, respectively (P value = 0.01). The mean cycloplegic spherical equivalent improved from + 3.5 ± 0.5 to + 0.25 ± 0.6 in Group (A) and from + 3.8 ± 0.6 to +0.75 ± 0.6 in Group (B) (P value = 0.02). The safety index was 1.1 in groups and the efficacy index, 1.01 in Group 1 and 0.98 in Group 2. The enhancement rate was 20.0% and 18.4%, respectively. Conclusion: Flap decentration in hyperopic laser correction provides more predictable results in correction of hyperopia.

. The initial reports of hyperopic LASIK (H-LASIK) showed mostly unsatisfactory results with considerable regression of the refractive results and a high incidence of loss of Best Corrected Visual Acuity (BCVA), primarily caused by small outer zone ablations [5].The rapid recovery of Uncorrected Visual Acuity (UCVA) was attributed to the good centration provided by the active tracking system of the laser.This was important because long treatment time in hyperopic corrections can produce severe rotational malpositions that can produce varying results [6].The use of planned off-center ablation to correct hyperopia may help in achieving better visual acuity than centered ablation [7].
The aim of this study is to evaluate the efficacy of corneal flap decentration during hyperopic LASIK in patients with offcentered corneal apex.

Material and methods
Forty four eyes of 22 patients with hyperopia were included in this study.The eyes were divided randomly into two groups.In group A (22 eyes); the flap was intentionally decentered during flap creation.In group B (22 eyes) were done without flap decentration.Preoperatively, a complete ophthalmic examination was performed including Uncorrected Visual Acuity (UCVA), Best Corrected Visual Acuity (BCVA), manifest and cycloplegic refraction.Spherical error ranged from + 1.00 to + 6.00 diopters, and refractive cylinder ranged from + 0.50 to + 2.5 D. Slit lamp biomicroscopy, applanation tonometry, and corneal topography were performed to all patients.Corneal topography was used to detect off-centered corneal apex.(Fig. 1).Emmetropia was the goal in all eyes.

Introduction
Laser in situ keratomileusis (LASIK) has been described as a means to correct hyperopia [1].Excimer laser correction of hyperopic refractive errors involves the para central removal of a negative meniscus of stromal tissue to indirectly produce central steepening of the anterior corneal surface [2].Many parameters, such as corneal curvature, optical zone size, and centration, must be taken into account even in correction of low grade hyperopia [3].The complications that limit hyperopic LASIK correction include decentration and regression, which can affect the predictability, safety, and efficacy of the treatment superiorly, exposing the stromal bed.Allegrtto 400Hz laser platform (Wave Light, Erlangen Germany) was used for laser ablation using T-CAT ablation profile to ensure centration of treatment around corneal apex.6 mm optical zone was applied in all cases.Care was taken to ensure that the stromal bed was dry before and during the ablation and that the undersurface of the flap was protected from the laser ablation.The interface was irrigated with a balanced salt solution; the flap was replaced.Adequate flap position was verified at the slit lamp immediately after surgery.
In group (B): the hyperopic LASIK correction was done but without flap decentration.Postoperative, patients were seen 1 day, 1 week, and 1, 3, and 6 months after surgery at which times UCVA, manifest refraction, BSCVA, corneal topography, and corneal flap status were determined.For the statistical analysis of results between the groups, a chi-squared test was used with the level of set at p < 0.05.
[Table 2] [Figure 1-2].The safety index was 1.1 in both groups and the efficacy index, 1.01 in Group (A) and 0.98 in Group (B).The enhancement rate was 20.0% and 18.4%, respectively.

Discussion
Laser correction of hyperopia involves the removal of a negative meniscus of stromal tissue that is thicker at the periphery than at its center.This reshapes the anterior corneal surface by steepening its curvature [1,8].The initial reports of hyperopic LASIK (H-LASIK) showed mostly unsatisfactory results with considerable regression of the refractive results and a high incidence of loss of BSCVA [3][4][5][6][7][8][9].In this study, one week after hyperopic LASIK correction, the mean UCVA was 0.9 in group A which undergone the operation with flap decentration while it was 0.8 in group B without flap decentration with significant statistically difference (p= 0.023).The group with flap decentration showed BCVA postoperatively 0.97 and the patients of other group had mean postoperative BCVA 0.8 with high significant difference (p= 0.01).
Zadok et al [10] on their study on 92 eyes undergone hyperopic LASIK correction, they divided the patients into 3 groups according to the degree of hyperopia: low hypeopia (+3.00 D), moderate hypeopia (+3 -+6.00 D) & high hyperopia (≥ + 6 D).They reported that spherical equivalent postoperatively was +0.33 in low hyperopic group, +0.21 D in moderate group & +1.62 D in high group.Carlos and Maria [11] compared the results of hyperopic laser in situ keratomileusis (LASIK) with a 5.9 mm optical zone (OZ) to those with smaller zones (4.4 to 5.5 mm).They operated 147 cases with 5.9 mm optical zone and 679 cases with smaller zone.They found that hyperopic LASIK with a 5.9 mm OZ in eyes with low, moderate and high hyperopia is more stable, predictable, and safer than hyperopic LASIK with smaller optical zone.

Table 1 :
Patients data